1. Field of the Invention
The present invention relates to a method of manufacturing a polysilicon thin film and a method of manufacturing a thin film transistor (TFT) having the thin film. More particularly, the present invention relates to a method of manufacturing a polysilicon thin film having improved electrical characteristics and a method of manufacturing a TFT having the thin film.
2. Description of the Related Art
A liquid crystal display (LCD) device includes a switching element. The switching element includes an amorphous silicon thin film transistor (a-Si TFT) or a polysilicon thin film transistor (poly-Si TFT). The LCD device having the poly-Si TFT has a faster operating speed than the LCD device having the a-Si TFT, thereby providing better image display quality than the LCD device having the a-Si TFT.
The poly-Si TFT is directly formed on a substrate, or an amorphous silicon thin film is crystallized to form the poly-Si TFT through heat treatment.
When a temperature of a glass substrate to be used for the LCD device rises above about 600° C., the glass substrate is deformed. This avoid this deformation, the amorphous silicon thin film is crystallized using an excimer laser. In the excimer laser annealing (ELA) process, a laser beam having a high energy is irradiated onto the amorphous silicon thin film for a period of tens of nanoseconds to crystallize the amorphous silicon thin film so that the glass substrate is not deformed.
When the amorphous silicon thin film is treated by the ELA process, silicon atoms in the amorphous silicon thin film are rearranged in a grain form to provide the poly-Si TFT with high electrical mobility. In the ELA process, the amorphous silicon thin film is melted and then solidified to form the poly-Si TFT. That is, the poly-Si TFT formed through the ELA process has high operating speed in a switched-on state.
However, a leakage current flows through an interface between polysilicon grains in a switched-off state. That is, silicon atoms at the interface are not securely combined with one another, causing an electron-hole to be formed at the interface, thereby generating a leakage current.